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What is anthelmintic resistance

Worms are considered to be resistant if they survive exposure to a
standard recommended dose of anthelmintic.
This ability to survive is then passed on to its offspring and the proportion of resistant worms increases over time. Anthelmintic resistance is not reversible, so farmers should use a post drench efficacy test to check the effectiveness of the wormers they use.
The percentage of resistant worms, and the number that survive treatment, increases with time as illustrated.
The speed which resistance develops depends on how carefully and sustainably
anthelmintics are used and how effectively sustainable practices are employed to address the three main selection pressures for anthelmintic resistance on worm populations in sheep:

under-dosing

over-use

treating sheep when the refugia population is small.

Source: SCOPS

Research from Wales Against Anthelmintic Resistance Development (WAARD) showed the majority of farms surveyed had a degree of resistance to all three older wormer classes2:

Act now, find out more about how you can incorporate Zolvix for your mid-late season break dose

Zolvix™ 25mg/ml oral solution is a broad spectrum anthelmintic for the treatment and control of gastro-intestinal nematode infections and associated diseases in sheep including lambs, hoggets, breeding rams and ewes. POM-VPS in UK. Information regarding the side effects, precautions, warnings and contra-indications can be found in product packaging and leaflets; further information can also be found in the Summary of Product Characteristics. Advice should be sought from the medicine prescriber prior to use. Zolvix, Elanco and the diagonal bar logo are trademarks of Elanco or its affiliates. Use medicines responsibly (http://www.noah.co.uk/responsible).